Legionnaire Disease and Pontiac Fever (cont.)
How is the diagnosis of Legionnaires' disease made?
Laboratory tests may include a modest increase in white blood cells, mild abnormalities in liver function studies, and even some decreased function of the kidneys, but these features can also be seen with a variety of different types of pneumonia. Chest X-rays often demonstrate abnormal densities (areas of that lungs that on the X-ray film appear whiter). However, it is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms and chest X-ray alone. Additional specific tests are required for diagnosis.
These other tests are specialized and are not routinely performed on people with fever or pneumonia. Several types of tests are available. The most useful test uses a urine sample to detect identifiable proteins of the Legionnaires' bacterium (Legionella antigens). Additionally, detecting the bacteria in a culture of the sputum may be helpful. Lastly, tests that compare antibody levels of
Legionella in two blood samples obtained three to six weeks apart showing a fourfold rise in the antibodies in the blood against the bacterium can be confirmatory after the disease is gone.
Because these tests complement each other, a positive result from
each test when Legionnaires' disease is suspected increases the
probability of confirming the diagnosis. However, because none of the
laboratory tests is 100% sensitive, the diagnosis of legionellosis is
not excluded even if one or more of the tests is negative. Of the
available tests, the most specific is culture isolation of the
bacterium from secretions from the respiratory tract.
Who develops legionellosis?
People of any age can develop Legionnaires' disease, but the illness
most often affects middle-aged and older people, particularly those
who smoke cigarettes or have chronic lung disease, as these individuals have a greater likelihood of developing any respiratory illness.
People at an increased risk for Legionnaires' disease also
include people whose immune systems are suppressed by diseases such
as cancer, kidney failure requiring dialysis, diabetes, or AIDS.
Those who take medications that suppress the immune system are also
at risk.
Pontiac fever most commonly occurs in people who are otherwise
healthy.
Next: What is the treatment for legionellosis? »
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